Lightning strikes of a plane can be a serious safety concern. Not only are high electrical currents directly dangerous to passengers and crew of the aircraft, but a lightning strike can damage or destroy the electrical and mechanical components of the aircraft, including sensitive avionics equipment. Because of this danger, commercial aircraft pilots tend to avoid flying through weather events that could cause lightning strikes. However, aircraft still encounter lightning, and its danger is undiminished. Because of such danger a pilot typically reports any observed lightning that contacts or is even adjacent the aircraft. After the flight, maintenance personnel conduct a visual inspection of the aircraft to determine whether the aircraft was actually struck by lightning, and note where the lightning entered and exited the plane.
One drawback to this after-action approach to lightning safety is that an aircraft pilot, traveling at cruising speed for the aircraft, may have merely observed a nearby lightning flash and may not know whether lightning actually struck the aircraft. Nevertheless, a lightning strike report is typically given to the on-ground maintenance crew to search for visible damage. This potentially time-consuming activity does not need to be done if an observed lightning strike has not actually struck the aircraft. Furthermore, because a lightning strike is instantaneous and because the aircraft pilot cannot observe the entire surface of the aircraft, a pilot may not have noticed a lightning strike that may have damaged the aircraft. Lastly, some lightning strikes are not powerful enough to destroy or permanently damage avionics equipment, but have sufficient power to temporarily upset the avionics equipment. If such upset equipment recovers and operates normally after the lightning strike, it is time-consuming and expensive to remove and fully test the equipment after the flight.
It is therefore an object of the invention to accurately detect when lightning has either struck an aircraft or a close lightning discharge has induced a damaging current into the aircraft structure or aircraft's electrical equipment system. Since peak lighting currents typically exceed 200 kiloamps with rise times in the 50 kiloamps per microsecond, lightning events that influence the aircraft and its electronic suite are very detectable. There is also a need to identify the portions of the airframe that may have been struck by lightning to reduce the amount of time needed for maintenance personnel to inspect possible airframe damage locations. In addition to the damage induced in the aircraft or its systems by lightning, lightning may also induce temporary failures or momentary upsets in aircraft equipment whether lightning is identified as the primary cause of the failure event or not. Identifying the failure or equipment upset as lightning induced can reduce the number of maintenance actions on equipment that do not need removal and repair.
Another object of the invention is to determine whether the strength of a lightning strike to an aircraft or an induced current from a nearby lightning strike is sufficient to require maintenance operations to electronic equipment on the aircraft.
A feature of the invention is an AC-coupled magnetic field detector, mounted to the exterior or in the radome of the aircraft, that measures the strength of change in magnetic fields with respect to time that are induced by either direct lightning strikes or nearby lightning events.
An advantage of the invention is that lightning induced events that potentially influence and aircraft or its systems can be accurately detected, measured, reported, and recorded for later maintenance use.